Golf ball

ABSTRACT

The invention provides a golf ball having a core, at least one intermediate layer encasing the core, and a cover. The intermediate layer is formed primarily of a specific ionomer resin composition that is highly neutralized. The cover is formed by injection molding a single resin blend composed primarily of a thermoplastic polyurethane and (g) a polyisocyanate compound in at least some portion of which all the isocyanate groups on the molecule are present in an unreacted state. The golf ball of the invention has a low spin rate on shots with a driver, enabling it to travel a good distance, and achieves a sufficient spin rate on shots with a short iron such as a wedge. The ball also has an excellent scuff resistance.

BACKGROUND OF THE INVENTION

The present invention relates to a golf ball which achieves a gooddistance on shots with a driver and has good spin properties on shotswith an iron, and which moreover has an excellent scuff resistance and agood durability.

Most golf balls currently in use are generally manufactured by using aprocess such as injection molding or compression molding to encase theperiphery of a solid core made primarily of a rubber such as dienerubber with a material composed primarily of, for example, urethaneresin or ionomer resin.

The major performance attributes required of golf balls includedistance, controllability, durability and feel on impact; balls havingthe highest levels of such attributes are constantly being sought. Inthis context, there has emerged among recent golf balls a succession ofballs with multilayer structures—typically three-piece balls. Providinga golf ball with a multilayer structure makes it possible to combinemany materials of differing properties; by assigning various functionsto the respective layers, a wide diversity of ball designs can beachieved.

Generally, when the distance traveled by a golf ball is regarded asimportant, the core or cover is formed so as to be rather hard, therebyincreasing the resilience of the ball when struck. Although the distancein such a case can be increased, when the ball is hit with a short ironsuch as a wedge, sufficient spin is not achieved, resulting in a poorcontrollability and a diminished feel. When this concern is addressed byforming the ball so as to be rather soft, sufficient spin is obtained onshots with a short iron, enabling controllability to be improved, inaddition to which the feel is also better. Yet, at the same time, makingthe ball softer lowers the rebound and also increases the spin rate onshots with a driver, making it difficult to achieve an increaseddistance. A cover made of an ionomer resin that does not readily crackand is somewhat soft is commonly used in such soft (low hardness) balls,but the resulting balls tend to have a poor scuff resistance. Sometimesthe cover is made instead of a thermoplastic polyurethane resin,although prior-art covers made of thermoplastic polyurethane resins alsohave a poor scuff resistance.

Although forming an intermediate layer of a highly neutralized ionomerresin composition in which the degree of neutralization of the ionomerresin has been increased through the addition of a basic inorganic metalcompound is effective for enhancing rebound and lowering the spin rate,the resulting ball often has a poor durability.

Hence, there exists a need for golf balls which satisfy the conflictingdemands for improved distance, controllability, durability and feel. Inparticular, there exists a desire for the development of a golf ballwhich increases the distance by keeping the spin rate low on shots witha driver; provides a suitable spin rate and good controllability onshots with an iron; and moreover has both an excellent scuff resistanceand an excellent durability.

Prior art relating to the present invention includes the three-piecesolid golf ball disclosed in JP-A 2001-79116 which has an outermostlayer composed of various types of thermoplastic elastomers to which aninorganic granular filler has been added. In addition, JP-A 2003-761discloses a golf ball in which an inorganic filler has been included ina cover material composed primarily of an ionomer resin, JP-A2003-126298 discloses a golf ball wherein an inorganic filler has beenincluded in a high-hardness resin, and JP-A 2008-49153 discloses a golfball having a cover composed of a polyurethane resin of improved scuffresistance. However, further improvement is desired.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golfball which achieves a good distance by suitably reducing the spin rateon shots with a driver, which achieves a suitable spin rate on shotswith a short iron, and which has an excellent scuff resistance and agood durability.

The inventors have conducted extensive investigations in order toachieve the above object. As a result, they have discovered that, in agolf ball having a core, at least one intermediate layer and a cover, byinjection-molding the cover from a single resin blend composed primarilyof (f) a thermoplastic polyurethane and (g) a polyisocyanate compound inat least some portion of which all the isocyanate groups on the moleculeare present in an unreacted state, and by combining such a cover with anintermediate layer made of a highly neutralized ionomer resincomposition obtained by adding a basic inorganic metal compound or thelike to a conventional ionomer resin so as to increase the degree ofneutralization, there can be obtained a golf ball which has a reducedspin rate on shots with a driver and a suitable degree of spin on shotswith a short iron, thus enabling both distance and controllability to beachieved, and which is also endowed with an excellent scuff resistanceand a good durability.

Accordingly, the invention provides the following golf balls.

[1] A golf ball comprising a core, at least one intermediate layer and acover, wherein the intermediate layer has a Shore D hardness of from 40to 60 and is formed primarily of a resin mixture having a degree ofneutralization of at least 70% and including:

100 parts by weight of a resin component composed of, in admixture,

-   -   a base resin of (a) an olefin-unsaturated carboxylic acid random        copolymer and/or a metal ion neutralization product of an        olefin-unsaturated carboxylic acid random copolymer blended        with (b) an olefin-unsaturated carboxylic acid-unsaturated        carboxylic acid ester random terpolymer and/or a metal ion        neutralization product of an olefin-unsaturated carboxylic        acid-unsaturated carboxylic acid ester random terpolymer in a        weight ratio of from 100:0 to 0:100, and

(e) a non-ionomeric thermoplastic elastomer

in a weight ratio of from 100:0 to 50:50;

(c) about 15 to about 150 parts by weight of a fatty acid and/or fattyacid derivative having a molecular weight of from 228 to 1500; and

(d) about 0.1 to about 17 parts by weight of a basic inorganic metalcompound capable of neutralizing un-neutralized acid groups in the baseresin and component (c), and the cover has a Shore D hardness of from 58to 65 and is formed by injection molding a single resin blend composedprimarily of (f) a thermoplastic polyurethane and (g) a polyisocyanatecompound in at least some portion of which all the isocyanate groups onthe molecule are present in an unreacted state.

[2] The golf ball of claim 1, wherein the hardness of the cover is equalto or greater than the hardness of the intermediate layer.[3] The golf ball of claim 1, wherein the resin blend which forms thecover includes (h) a thermoplastic elastomer other than a thermoplasticpolyurethane.[4] The golf ball of claim 4, wherein some portion of the isocyanategroups in the polyisocyanate compound (g) included in the resin blendprior to injection molding form bonds with active hydrogens in component(f) and/or component (h), and the remaining isocyanate groups arepresent within the resin blend in an unreacted state.[5] The golf ball of claim 4, wherein the components in the resin blendwhich forms the cover have a compositional ratio, expressed as a weightratio, of (f):(g):(h)=100:2 to 50:0 to 50.[6] The golf ball of claim 4, wherein the components in the resin blendwhich form the cover have a compositional ratio, expressed as a weightratio, of (f):(g):(h)=100:2 to 30:8 to 50.[7] The golf ball of claim 1, wherein the resin blend which forms thecover has a melt mass flow rate (MFR) value at 210° C. of at least 5g/10 min.[8] The golf ball of claim 1, wherein the polyisocyanate compound ofcomponent (g) is one or more polyisocyanate compound selected from thegroup consisting of 4,4′-diphenylmethane diisocyanate, 2,4- (or)2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylenediisocyanate, 1,5-naphthylene diisocyanate, tetramethylxylenediisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethanediisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate,isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylenediisocyanate and dimer acid diisocyanate.[9] The golf ball of claim 1, wherein the polyisocyanate compound ofcomponent (g) is one or more polyisocyanate compound selected from thegroup consisting of 4,4′-diphenylmethane diisocyanate,dicyclohexylmethane diisocyanate and isophorone diisocyanate.[10] The golf ball of claim 4, wherein the thermoplastic elastomer ofcomponent (h) is one or more thermoplastic elastomer selected from thegroup consisting of polyester elastomers, polyamide elastomers, ionomerresins, styrene block elastomers, hydrogenated styrene-butadienerubbers, styrene-ethylene/butylene-ethylene block copolymers andmodified forms thereof, ethylene-ethylene/butylene-ethylene blockcopolymers and modified forms thereof, styrene-ethylene/butylene-styreneblock copolymers and modified forms thereof, ABS resins, polyacetals,polyethylenes and nylon resins.[11] The golf ball of claim 4, wherein the thermoplastic elastomer ofcomponent (h) is one or more selected from the group consisting ofpolyester elastomers, polyamide elastomers and polyacetals.[12] The golf ball of claim 1, wherein the ball has a plurality ofdimples formed on a surface thereof, which dimples number in all from250 to 392 and have a total volume of from 400 to 750 mm³.

BRIEF DESCRIPTION OF THE DIAGRAMS

FIG. 1 is a top view of a golf ball showing an Arrangement (I) ofdimples used in the examples of the invention and in the comparativeexamples.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described in greater detail below.

The golf ball of the present invention has a solid core, at least oneintermediate layer, and a cover.

In the invention, the solid core may be formed using a known rubbercomposition. Although not subject to any particular limitation, suitablerubber compositions include those formulated as shown below.

A rubber core which has been molded and vulcanized from a rubbercomposition made up primarily of a commonly used rubber base may beemployed as the core in the present invention. Specifically, the core isformed using a molded and vulcanized rubber composition obtained bycompounding the following with a base rubber: a crosslinking agent, avulcanizing agent and, optionally, additives such as organosulfurcompounds, antioxidants and fillers.

Polybutadiene is preferably used as the base rubber of the rubbercomposition that forms the core. It is preferable to usecis-1,4-polybutadiene having a cis structure of at least 40% as thepolybutadiene. If desired, natural rubber, polyisoprene rubber,styrene-butadiene rubber or ethylene-propylene-diene rubber, forexample, may be suitably compounded together with the polybutadiene inthe base rubber.

An α,β-unsaturated carboxylic acid such as zinc methacrylate or zincacrylate may be included as a co-crosslinking agent in the rubbercomposition. The use of zinc acrylate is especially preferred. Theamount in which these unsaturated carboxylic acids are included per 100parts by weight of the base rubber may be set to at least 10 parts byweight, and especially at least 15 parts by weight. The upper limit isset to preferably not more than 40 parts by weight, and most preferablynot more than 35 parts by weight.

A vulcanizing agent is included in the above rubber composition. Anorganic peroxide is preferably used as the vulcanizing agent. Theorganic peroxide, an illustrative example of which is dicumyl peroxide,may be a single type used alone or may be a mixture of two or moretypes. The organic peroxide may be a commercially available product,specific examples of which include Perhexa 3M (produced by NOFCorporation), Percumyl D (NOF Corporation), and Luperco 231XL andLuperco 101XL (both produced by Atochem Co.). The amount of vulcanizingagent included may be set to more than 0, and may be set to preferablyat least 0.1 part by weight per 100 parts by weight of the base rubber.The upper limit in the amount of the vulcanizing agent, although notsubject to any particular limitation, may be set to preferably not morethan 2 parts by weight, and more preferably not more than 1.5 parts byweight, per 100 parts by weight of the base rubber.

In the invention, an organosulfur compound may be included so as tofurther improve the core resilience. Specifically, it is recommendedthat thiophenols, thionaphthols, halogenated thiophenols or metal saltsthereof be included. Illustrative examples includepentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol,p-chlorothiophenol, the zinc salt of pentachlorothiophenol, anddiphenylpolysulfides, dibenzylpolysulfides, dibenzoylpolysulfides,dibenzothiazoylpolysulfides and dithiobenzoylpolysulfides having from 2to 4 sulfurs. The use of diphenyldisulfide or the zinc salt ofpentachlorothiophenol is especially preferred.

In addition, an antioxidant may be included. Examples of commercialproducts include Nocrac NS-6, Nocrac NS-30 and Nocrac SP-N (Ouchi ShinkoChemical Industry Co., Ltd.), and Yoshinox 425 (Yoshitomo PharmaceuticalIndustries, Ltd.). These may be used singly or as combinations of two ormore thereof.

The filler is not subject to any particular limitation. For example,zinc oxide, barium sulfate and calcium carbonate may be suitablyincluded.

The core-forming rubber composition which includes the above ingredientsis prepared by mastication using a conventional mixer, such as a Banburymixer or a roll mill. In cases where the core is molded using such arubber composition, molding may be carried out by compression molding orinjection molding using a specific core-forming mold. The resultingmolded body is then heated and cured under temperature conditionssufficient for the crosslinking agent and co-crosslinking agent includedin the rubber composition to act, thereby giving a core having aspecific hardness profile. The vulcanization conditions are not subjectto any particular limitation. For example, when dicumyl peroxide is usedas the crosslinking agent and zinc acrylate is used as theco-crosslinking agent, the conditions are generally set to about 100 to200° C., and especially 130 to 180° C., for 10 to 40 minutes, andespecially 12 to 20 minutes.

The diameter of the core obtained by the above manufacturing method,although not subject to any particular limitation, is preferably atleast 36.5 mm, more preferably at least 36.8 mm, and even morepreferably at least 37.2 mm. The upper limit in the diameter, althoughnot subject to any particular limitation, is preferably not more than 40mm, more preferably not more than 39.7 mm, and even more preferably notmore than 39.5 mm.

In the present invention, although not subject to any particularlimitation, the core has a deformation, when compressed under a finalload of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), ofpreferably at least 3.5 mm but not more than 6.0 mm. The lower limit inthis deformation is more preferably at least 4.0 mm, and even morepreferably at least 4.3 mm. The upper limit is more preferably not morethan 5.5 mm, and even more preferably not more than 5.0 mm. If the coreis softer than the above value (large deformation), the core resiliencewill diminish. Conversely, if the core is harder than the above value(small deformation), the feel of the ball may worsen.

The structure of the core is not limited to one layer, and may be amultilayer structure of two or more layers. By giving the core amultilayer structure, it is possible to reduce the spin rate on shotswith a driver, and it is possible to further increase the distancetraveled by the ball. In addition, the spin properties and feel of theball at the time of impact can be further improved. In such cases, thecore will have at least an inner core layer (center sphere) and an outercore layer.

The golf ball of the invention has at least one intermediate layer whichencases the core, and a cover which encases the intermediate layer. Thematerials of the intermediate layer and cover are described in detailbelow.

In the present invention, the intermediate layer is formed primarily ofa resin composition which includes: 100 parts by weight of a resincomponent composed of, in admixture,

a base resin of (a) an olefin-unsaturated carboxylic acid randomcopolymer and/or a metal ion neutralization product of anolefin-unsaturated carboxylic acid random copolymer blended with (b) anolefin-unsaturated carboxylic acid-unsaturated carboxylic acid esterrandom terpolymer and/or a metal ion neutralization product of anolefin-unsaturated carboxylic acid-unsaturated carboxylic acid esterrandom terpolymer in a weight ratio of from 100:0 to 0:100, and

(e) a non-ionomeric thermoplastic elastomer

in a weight ratio of from 100:0 to 50:50;(c) about 15 to about 150 parts by weight of a fatty acid and/or fattyacid derivative having a molecular weight of from 228 to 1500; and(d) about 0.1 to about 17 parts by weight of a basic inorganic metalcompound capable of neutralizing un-neutralized acid groups in the baseresin and component (c)

Above components (a) to (e) are described below.

Component (a) and component (b) serve as the base resin of the resincomposition which forms the intermediate layer. Component (a) is anolefin-unsaturated carboxylic acid random copolymer and/or a metal ionneutralization product of an olefin-unsaturated carboxylic acid randomcopolymer, and component (b) is an olefin-unsaturated carboxylicacid-unsaturated carboxylic acid ester random terpolymer and/or a metalion neutralization product of an olefin-unsaturated carboxylicacid-unsaturated carboxylic acid ester random terpolymer. In the presentinvention, either of above components (a) and (b) may be used singly orboth may used in combination.

Here, the olefin in above component (a) and component (b) generally hasat least two carbons but not more than 8 carbons, and most preferablynot more than 6 carbons. Illustrative examples include ethylene,propylene, butene, pentene, hexene, heptene and octene. Ethylene isespecially preferred.

Examples of the unsaturated carboxylic acid include acrylic acid,methacrylic acid, maleic acid and fumaric acid. Acrylic acid andmethacrylic acid are especially preferred.

In addition, the unsaturated carboxylic acid ester included in abovecomponent (b) is preferably a lower alkyl ester of the above unsaturatedcarboxylic acid, illustrative examples of which include methylmethacrylate, ethyl methacrylate, propyl methacrylate, butylmethacrylate, methyl acrylate, ethyl acrylate, propyl acrylate and butylacrylate. Butyl acrylate (n-butyl acrylate, i-butyl acrylate) isespecially preferred.

The random copolymer of component (a) and component (b) may be obtainedby the random copolymerization of the above components by a knownmethod. Here, the content (acid content) of the unsaturated carboxylicacid included in the random copolymer, although not subject to anyparticular limitation, may be set to preferably at least 2 wt %, morepreferably at least 6 wt %, and even more preferably at least 8 wt %. Itis recommended that the upper limit in the unsaturated carboxylic acidcontent (acid content), although not subject to any particularlimitation, be preferably not more than 25 wt %, more preferably notmore than 20 wt %, and even more preferably not more than 15 wt %.

The random copolymer neutralization products of components (a) and (b)may be obtained by neutralizing some of the acid groups in the aboverandom copolymer with metal ions. Here, illustrative examples of metalions which neutralize the acid groups include Na⁺, K⁺, Li⁺, Zn⁺⁺, Cu⁺⁺,Mg⁺⁺, Ca⁺⁺, Co⁺⁺, Ni⁺⁺ and Pb⁺⁺. Of these, preferred use may be made ofNe⁺, Li⁺, Zn⁺⁺ and Mg⁺⁺; Mg⁺⁺ and Zn⁺⁺ are especially recommended. Thedegree of neutralization of the random copolymer by these metal ions isnot subject to any particular limitation. Such neutralization productsmay be obtained by a known method. For example, these metal ions may beintroduced into the random copolymer by using compounds such asformates, acetates, nitrates, carbonates, bicarbonates, oxides,hydroxides or alkoxides thereof.

A commercial product may be used as above component (a). Illustrativeexamples include Nucrel AN4311, Nucrel AN4318, Nucrel AN4319, Nucrel1560 and Nucrel AN4213C (all produced by DuPont-Mitsui PolychemicalsCo., Ltd.).

Likewise, a commercial product may be used as above component (b).Illustrative examples include Himilan 1554, Himilan 1557, Himilan 1601,Himilan 1605, Himilan 1706, Himilan 1855, Himilan 1856 and HimilanAM7316 (all produced by DuPont-Mitsui Polychemicals Co., Ltd.); andSurlyn 6320, Surlyn 7930 and Surlyn 8120 (all produced by E.I. DuPont deNemours & Co.). The use of a zinc-neutralized ionomer resin (e.g.,Himilan AM7316) is especially preferred.

Above component (a) and component (b) may be used individually or bothmay be used in combination as the base resin of the above intermediatelayer-forming resin composition. The mixing ratio of these twocomponents, expressed by weight as (a):(b), is from 100:0 to 0:100.Although not subject to any particular limitation, the mixing ratio ispreferably from 80:20 to 50:50, and more preferably from 70:30 to 60:40.

Component (c) is a fatty acid or fatty acid derivative having amolecular weight of at least 228. This component contributes toimproving the flow properties of the resin composition; it has a verysmall molecular weight compared with the thermoplastic resin of abovecomponent (a), and thus contributes to a marked decrease in the meltviscosity of the mixture. Because the fatty acid (or fatty acidderivative) in the present invention has a molecular weight of 228 ormore and contains a high content of acid groups (or derivative moietiesthereof), its addition results in little loss in resilience.

The fatty acid or fatty acid derivative serving as component (c) has amolecular weight which is at least 228, preferably at least 256, morepreferably at least 280, and even more preferably at least 300, with anupper limit of not more than 1,500, preferably not more than 1,000, morepreferably not more than 600, and even more preferably not more than500. Here, if the molecular weight is too low, it will be impossible toachieve an improvement in the heat resistance, in addition to which thecontent of acid groups will be so high that interactions with acidgroups present in the base resin may lower the flow-improving effects.On the other hand, if the molecular weight is too high, a distinctflow-improving effect may not appear.

Specific examples of the fatty acid serving as component (c) includestearic acid, 12-hydroxystearic acid, behenic acid, oleic acid, linoleicacid, linolenic acid, arachidic acid and lignoceric acid. Of these,preferred use may be made of stearic acid, arachidic acid, behenic acidand lignoceric acid.

The fatty acid derivative is exemplified by derivatives in which theproton on the acid group of the fatty acid has been substituted.Exemplary fatty acid derivatives of this type include metallic soaps inwhich the proton has been substituted with a metal ion. Metal ions thatmay be used in such metallic soaps include Li⁺, Ca⁺⁺, Mg⁺⁺, Zn⁺⁺, Mn⁺⁺,Al⁺⁺⁺, Ni⁺⁺, Fe⁺⁺, Fe⁺⁺⁺, Cu⁺⁺, Sn⁺⁺, Pb⁺⁺ and Co⁺⁺. Of these, Ca⁺⁺,Mg⁺⁺ and Zn⁺⁺ are especially preferred.

Specific examples of fatty acid derivatives that may be used ascomponent (c) include magnesium stearate, calcium stearate, zincstearate, magnesium 12-hydroxystearate, calcium 12-hydroxystearate, zinc12-hydroxystearate, magnesium arachidate, calcium arachidate, zincarachidate, magnesium behenate, calcium behenate, zinc behenate,magnesium lignocerate, calcium lignocerate and zinc lignocerate. Ofthese, magnesium stearate, calcium stearate, zinc stearate, magnesiumarachidate, calcium arachidate, zinc arachidate, magnesium behenate,calcium behenate, zinc behenate, magnesium lignocerate, calciumlignocerate and zinc lignocerate are preferred.

The amount of component (c) used per 100 parts by weight of abovecomponent (a) and/or component (b) (referred to below as the “baseresin”) is from about 50 to about 150 parts by weight. The lower limitis preferably at least about 81 parts by weight, and the upper limit ispreferably not more than about 120 parts by weight.

Use may also be made of known metallic soap-modified ionomers (see, forexample, U.S. Pat. No. 5,312,857, U.S. Pat. No. 5,306,760 andInternational Disclosure WO 98/46671) when using above component (a)and/or component (b), and component (c).

The basic inorganic filler of component (d) is included to neutralizethe acid groups in above component (a) and/or component (b), and incomponent (c). When above component (d) is not included, and inparticular when a metal-modified ionomer resin alone (e.g., a metalsoap-modified ionomer resin of the type mentioned in the foregoingpatent publications, alone) is mixed under applied heat, as mentionedbelow, the metallic soap and unneutralized acid groups present on theionomer undergo exchange reactions, generating a fatty acid. Because thefatty acid has a low thermal stability and readily vaporizes duringmolding, it causes molding defects. Moreover, if the fatty acid thusgenerated deposits on the surface of the molded material, itsubstantially lowers paint film adhesion.

(1) unneutralized acid group present on the ionomer resin(2) metallic soap(3) fatty acidX: metal atom

To solve such problems, it is essential to include as component (d) abasic inorganic metal compound which neutralizes acid groups present inabove component (a) and/or component (b), and in component (c). Theinclusion of component (d) confers excellent properties. Namely, theacid groups in above component (a) and/or component (b) and in component(c) are neutralized, and synergistic effects from the inclusion of eachof these components increase the thermal stability of the resincomposition while at the same time imparting a good moldability, andalso enhance the resilience as a golf ball-forming material.

It is recommended that above component (d) be a basic inorganic metalcompound—preferably a monoxide—which is capable of neutralizing acidgroups in above component (a) and/or component (b), and in component(c). Because such compounds have a high reactivity with the ionomerresin and the reaction by-products contain no organic matter, the degreeof neutralization of the resin composition can be increased without aloss of thermal stability.

The metal ions used here in the basic inorganic metal compound areexemplified by Li⁺, Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, Zn⁺⁺, Al⁺⁺⁺, Ni⁺, Fe⁺⁺, Fe⁺⁺⁺,Cu⁺⁺, Mn⁺⁺, Sn⁺⁺, Pb⁺⁺ and Co⁺⁺. Illustrative examples of the inorganicmetal compound include basic inorganic fillers containing these metalions, such as magnesium oxide, magnesium hydroxide, magnesium carbonate,zinc oxide, sodium hydroxide, sodium carbonate, calcium oxide, calciumhydroxide, lithium hydroxide and lithium carbonate. Of these, as notedabove, a monoxide is preferred. The use of magnesium oxide, which has ahigh reactivity with ionomer resins, is especially preferred in thepresent invention.

Component (d) is included in an amount, per 100 parts by weight of theabove resin component, of from about 0.1 to about 17 parts by weight.Here, the lower limit is preferably at least 0.5 part by weight, and theupper limit is preferably not more than about 15 parts by weight. If theamount of above component (d) included is too low, improvements inthermal stability and resilience will not be observed. On the otherhand, if the amount is too high, the thermal resistance of thecomposition may instead decline due to excessive basic inorganic metalcompound.

The non-ionomeric thermoplastic elastomer serving as component (e) isincluded to further improve the feel of the ball on impact and therebound. Illustrative examples include thermoplastic elastomers such asthermoplastic polyester elastomers, thermoplastic block copolymers andthermoplastic urethanes.

The above component (e) is included in an amount, expressed as a weightratio of the above-described base resin to component (e), of from 100:0to 50:50.

From the standpoint of processability, it is desirable for theintermediate layer-forming resin composition which includes abovecomponents (a) to (e) to have a melt index (measured in accordance withJIS-K6760 at a test temperature of 190° C. and a test load of 21 N (2.16kgf)) of at least 0.5 g/10 min, preferably at least 0.8 g/10 min, andmore preferably at least 1.0 g/min. The upper limit in this melt indexis not more than 20 g/10 min, and more preferably not more than 15 g/10min. If the melt index of the resin composition is too low, theprocessability may markedly decrease.

Although the specific gravity of this resin composition itself is notsubject to any particular limitation, it may be set to preferably atleast 0.9. The upper limit of this specific gravity, although notsubject to any particular limitation, is preferably set to not more than1.3, and more preferably set to no more than 1.2.

The above resin composition is obtained by mixing under applied heat theabove-described component (a) and/or component (b), component (c),component (d) and component (e), and has an optimized melt index. It isrecommended that at least 70 mol %, preferably at least 80 mol %, andmore preferably at least 90 mol %, of the acid groups in the resincomposition be neutralized. A high degree of neutralization morereliably suppresses the exchange reactions that pose a problem in theabove-described cases where the base resin and the fatty acid (or fattyacid derivative) alone are used, thus making it possible to prevent thegeneration of fatty acids. As a result, a material can be obtained whichhas a markedly increased thermal stability, a good moldability, and asubstantially higher resilience than conventional ionomer resins.

An inorganic granular filler may be optionally included in the resincomposition so as to further improve durability. This inorganic granularfiller may be a known inorganic granular filler and is not subject toany particular limitation, although the use of titanium dioxide andbarium sulfate is preferred in the present invention. The amount per 100parts by weight of the above base resin is set to preferably at least 5parts by weight, and more preferably at least 9 parts by weight. Theupper limit is preferably not more than 36 parts by weight, and morepreferably not more than 26 parts by weight.

Various additives may be optionally added to the resin compositioncontaining components (a) to (e). Additives which may be used includepigments, antioxidants, ultraviolet absorbers and light stabilizers.

The method used to form the intermediate layer may be a known method andis not subject to any particular limitation. For example, a method maybe employed which involves placing a prefabricated core within a mold,then melting under applied heat, or mixing and melting under appliedheat, and subsequently injection-molding the intermediate layer-formingresin composition.

The Shore D hardness of the intermediate layer is preferably at least40, and more preferably at least 43. The upper limit is preferably notmore than 65, and more preferably not more than 60. At a Shore Dhardness below 40, the rebound may decrease, whereas at more than 65,the ball may crack more easily, resulting in a poor durability.

The thickness of the intermediate layer is not subject to any particularlimitation, although it is recommended that the thickness be at least0.8 mm, and especially 1 mm. It is recommended that the upper limit inthe intermediate layer thickness be not more than 4.0 mm, and especiallynot more than 3.0 mm.

The specific gravity of the intermediate layer, although not subject toany particular limitation, is preferably at least 0.9, and morepreferably at least 0.95. The upper limit in the specific gravity alsois not subject to any particular limitation, although a value of notmore than 1.3, and especially not more than 1.15, is recommended. If thespecific gravity is too large, thorough dispersion and mixing may becomedifficult to carry out. On the other hand, if the specific gravity istoo small, there may be cases where.

Moreover, the hardness of the intermediate layer is set to a Shore Dvalue of preferably from 40 to 60, and more preferably from 43 to 60. Atan intermediate layer hardness having a Shore D value of less than 40,the resilience may be diminish; on the other hand, at a Shore D valuegreater than 60, the ball may have a diminished feel on impact and maycrack more easily.

The construction of the intermediate layer is not limited to a singlelayer. If necessary, two or more intermediate layers having differentproperties may be formed within the above-described range. By forming aplurality of intermediate layers, the spin rate on shots with a drivercan be reduced, enabling an even greater increase in distance to beachieved. Also, the spin properties and feel at the time of impact canbe further improved.

The golf ball of the invention is arrived at by forming a cover over,and thereby encasing, the outside of the intermediate layer. The coveris composed primarily of a thermoplastic polyurethane, and is formedfrom a single resin blend composed primarily of (f) a thermoplasticpolyurethane and (g) a polyisocyanate compound. Golf balls which usesuch a cover made of a thermoplastic polyurethane have a high reboundand an excellent spin performance and scuff resistance. Moreover, thecover-forming material has high flow properties and an excellentproductivity.

As used herein, a “single” resin blend means that the cover is molded,not by feeding as the resin blend a plurality of pellet types, but byfeeding to injection molding one type of pellet obtained by formulatinga plurality of ingredients into single pellets.

This cover is composed primarily of (f) a thermoplastic polyurethane and(g) a polyisocyanate compound. Specifically, it is recommended that thecombined weight of components (f) and (g) be at least 60%, andpreferably at least 70%, of the overall weight of the cover layer.

The thermoplastic polyurethane (f) is described. This thermoplasticpolyurethane has a structure which includes soft segments made of apolymeric polyol that is a long-chain polyol (polymeric glycol), andhard segments made of a chain extender and a polyisocyanate compound.Here, the long-chain polyol used as a starting material is not subjectto any particular limitation, and may be any that is used in the priorart relating to thermoplastic polyurethanes. Exemplary long-chainpolyols include polyester polyols, polyether polyols, polycarbonatepolyols, polyester polycarbonate polyols, polyolefin polyols, conjugateddiene polymer-based polyols, castor oil-based polyols, silicone-basedpolyols and vinyl polymer-based polyols. These long-chain polyols may beused singly or as combinations of two or more thereof. Of the long-chainpolyols mentioned here, polyether polyols are preferred because theyenable the synthesis of thermoplastic polyurethanes having a highrebound resilience and excellent low-temperature properties.

Illustrative examples of the above polyether polyol includepoly(ethylene glycol), poly(propylene glycol), poly(tetramethyleneglycol) and poly(methyltetramethylene glycol) obtained by thering-opening polymerization of a cyclic ether. The polyether polyol maybe used singly or as a combination of two or more polyether polyols. Ofthese, poly(tetramethylene glycol) and/or poly(methyltetramethyleneglycol) are preferred.

It is preferable for these long-chain polyols to have a number-averagemolecular weight in a range of 1,500 to 5,000. By using a long-chainpolyol having a number-average molecular weight within this range, golfballs made of a thermoplastic polyurethane composition having variousexcellent properties such as resilience and manufacturability can bereliably obtained. The number-average molecular weight of the long-chainpolyol is more preferably in a range of 1,700 to 4,000, and even morepreferably in a range of 1,900 to 3,000.

As used herein, “number-average molecular weight of the long-chainpolyol” refers to the number-average molecular weight computed based onthe hydroxyl number measured in accordance with JIS K-1557.

Suitable chain extenders include those used in the prior art relating tothermoplastic polyurethanes. For example, low-molecular-weight compoundswhich have a molecular weight of 400 or less and bear on the moleculetwo or more active hydrogen atoms capable of reacting with isocyanategroups are preferred. Illustrative, non-limiting, examples of the chainextender include 1,4-butylene glycol, 1,2-ethylene glycol,1,3-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. Ofthese chain extenders, aliphatic diols having 2 to 12 carbons arepreferred, and 1,4-butylene glycol is especially preferred.

The polyisocyanate compound is not subject to any particular limitation;preferred use may be made of one employed in the prior art relating tothermoplastic polyurethanes. Specific examples include one or moreselected from the group consisting of 4,4′-diphenylmethane diisocyanate,2,4- or 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylenediisocyanate, 1,5-naphthylene diisocyanate, tetramethylxylenediisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethanediisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate,isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylenediisocyanate and dimer acid diisocyanate. Depending on the type ofisocyanate used, the crosslinking reaction during injection molding maybe difficult to control. In the practice of the invention, to provide abalance between stability at the time of production and the propertiesthat are manifested, it is most preferable to use 4,4′-diphenylmethanediisocyanate, which is an aromatic diisocyanate.

It is most preferable for the thermoplastic polyurethane serving ascomponent (f) to be a thermoplastic polyurethane synthesized using apolyether polyol as the long-chain polyol, using an aliphatic diol asthe chain extender, and using an aromatic diisocyanate as thepolyisocyanate compound. It is desirable, though not essential, for thepolyether polyol to be a polytetramethylene glycol having anumber-average molecular weight of at least 1,900, for the chainextender to be 1,4-butylene glycol, and for the aromatic diisocyanate tobe 4,4′-diphenylmethane diisocyanate.

The mixing ratio of active hydrogen atoms to isocyanate groups in theabove polyurethane-forming reaction can be controlled within a desirablerange so as to make it possible to obtain a golf ball which is composedin part of a thermoplastic polyurethane composition and has variousimproved properties, such as rebound, spin performance, scuff resistanceand manufacturability. Specifically, in preparing a thermoplasticpolyurethane by reacting the above long-chain polyol, polyisocyanatecompound and chain extender, it is desirable to use the respectivecomponents in proportions such that the amount of isocyanate groups onthe polyisocyanate compound per mole of active hydrogen atoms on thelong-chain polyol and the chain extender is from 0.95 to 1.05 moles.

No particular limitation is imposed on the method of preparing thethermoplastic polyurethane used as component (f). Production may becarried out by either a prepolymer process or a one-shot process inwhich the long-chain polyol, chain extender and polyisocyanate compoundare used and a known urethane-forming reaction is effected. Of these, aprocess in which melt polymerization is carried out in a substantiallysolvent-free state is preferred. Production by continuous meltpolymerization using a multiple screw extruder is especially preferred.

Illustrative examples of the thermoplastic polyurethane serving ascomponent (f) include commercial products such as Pandex T8295, PandexT8290, Pandex T8260, Pandex T8295 and Pandex T8290 (all available fromDIC Bayer Polymer, Ltd.).

Next, concerning the polyisocyanate compound used as component (g), itis essential that, in at least some portion thereof prior to injectionmolding, all the isocyanate groups on the molecule remain in anunreacted state. That is, polyisocyanate compound in which all theisocyanate groups on the molecule remain in a completely free state mustbe present in the single resin blend prior to injection molding. Such apolyisocyanate compound may be present together with a polyisocyanatecompound in which only some of the isocyanate groups on the molecule arein a free state.

Various isocyanates may be employed without particular limitation asthis polyisocyanate compound. Illustrative examples include one or moreselected from the group consisting of 4,4′-diphenylmethane diisocyanate,2,4- or 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylenediisocyanate, 1,5-naphthylene diisocyanate, tetramethylxylenediisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethanediisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate,isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylenediisocyanate and dimer acid diisocyanate. Of the above group ofisocyanates, the use of 4,4′-diphenylmethane diisocyanate,dicyclohexylmethane diisocyanate and isophorone diisocyanate ispreferable in terms of the balance between the influence onprocessability of such effects as the rise in viscosity that accompaniesreaction with the thermoplastic polyurethane serving as component (f)and the physical properties of the resulting golf ball cover material.

In the cover of the inventive golf ball, although not an essentialconstituent, a thermoplastic elastomer other than the above-describedthermoplastic polyurethane may additionally be included as component (h)together with components (f) and (g). Including this component (h) inthe above resin composition enables the flow properties of the resinblend to be further improved and enables increases to be made in variousproperties required of golf ball cover materials, such as resilience andscuff resistance.

Component (h), which is a thermoplastic elastomer other than the abovethermoplastic polyurethane, is exemplified by one or more thermoplasticelastomer selected from among polyester elastomers, polyamideelastomers, ionomer resins, styrene block elastomers, hydrogenatedstyrene-butadiene rubbers, styrene-ethylene/butylene-ethylene blockcopolymers and modified forms thereof,ethylene-ethylene/butylene-ethylene block copolymers and modified formsthereof, styrene-ethylene/butylene-styrene block copolymers and modifiedforms thereof, ABS resins, polyacetals, polyethylenes and nylon resins.The use of polyester elastomers, polyamide elastomers and polyacetals isespecially preferred because the resilience and scuff resistance areenhanced, owing to reactions with isocyanate groups, while a goodmanufacturability is retained.

The relative proportions of above components (f), (g) and (h) are notsubject to any particular limitation. However, to fully and effectivelyachieve the objects of the invention, it is preferable for the weightratio (f):(g):(h) of the respective components to be 100:2 to 50:0 to50, and more preferably 100:2 to 30:8 to 50.

In the present invention, the cover-forming resin blend is prepared bymixing together component (f), component (g), and also optionalcomponent (h). It is necessary to select the mixing conditions at thistime such that at least some polyisocyanate compound in which all theisocyanate groups on the molecule remain in an unreacted state ispresent in the polyisocyanate compound. For example, treatment such asmixture in an inert gas (e.g., nitrogen) or in a vacuum state must befurnished. The resin blend is then injection-molded around a core whichhas been placed in a mold. For easy, trouble-free handling, it ispreferable that the resin blend be formed into pellets having a lengthof 1 to 10 mm and a diameter of 0.5 to 5 mm. A sufficient number ofisocyanate groups in an unreacted state remain within these resinpellets; while the resin blend is being injection-molded about the core,or due to post-treatment such as annealing thereafter, the unreactedisocyanate groups react with component (f) and component (h) to form acrosslinked material.

In addition, various additives may also be optionally included in thiscover-forming resin blend. For example, pigments, dispersants,antioxidants, light stabilizers, ultraviolet absorbers, and partingagents may be suitably included.

The melt mass flow rate (MFR) of this resin blend at 210° C. is notsubject to any particular limitation. However, to increase the flowproperties and manufacturability, the MFR is preferably at least 5 g/10min, and more preferably at least 6 g/10 min. If the melt mass flow rateof the resin blend is low, the flow properties will decrease, which maycause eccentricity during injection molding and may also lower thedegree of freedom in the thickness of the cover that can be molded. Themeasured value of the melt mass flow rate is obtained in accordance withJIS K-7210 (1999 edition).

The method of molding the cover layer may involve feeding theabove-described resin blend to an injection-molding machine andinjecting the molten resin blend around the core. Although the moldingtemperature in this case will vary depending on the type ofthermoplastic polyurethane, the molding temperature is generally in arange of from 150 to 250° C.

When injection molding is carried out, it is desirable though notessential to carry out molding in a low-humidity environment such as bypurging with an inert gas (e.g., nitrogen) or a low-humidity gas (e.g.,low dew-point dry air), or by vacuum treating, some or all places on theresin paths from the resin feed area to the mold interior. Illustrative,non-limiting, examples of the medium used for transporting the resininclude low-humidity gases such as low dew-point dry air or nitrogen. Bycarrying out molding in such a low-humidity environment, reaction by theisocyanate groups is kept from proceeding before the resin has beencharged into the mold interior. As a result, polyisocyanate in which theisocyanate groups are to some degree in an unreacted state can beincluded within the resin blend, thus making it possible to reducevariable factors such as an unwanted rise in viscosity and enabling theactual crosslinking efficiency to be enhanced.

Techniques that may be used to confirm the presence of polyisocyanatecompound in an unreacted state within the resin blend prior to injectionmolding about the core include those which involve extraction with asuitable solvent that selectively dissolves out only the polyisocyanatecompound. An example of a simple and convenient method is one in whichconfirmation is carried out by simultaneous thermogravimetric anddifferential thermal analysis (TG-DTA) measurement in an inertatmosphere. For example, when the resin blend (cover material) used inthe invention is heated in a nitrogen atmosphere at a temperatureramp-up rate of 10° C./min, a gradual drop in the weight ofdiphenylmethane diisocyanate can be observed from about 150° C. On theother hand, in a resin sample in which the reaction between thethermoplastic polyurethane material and the isocyanate mixture has beencarried out to completion, a weight drop is not observable from about150° C., but a weight drop is observable from about 230 to 240° C.

After the resin blend has been molded as described above to form acover, its properties as a golf ball cover can be further improved bycarrying out annealing so as to induce the crosslinking reaction toproceed further. “Annealing,” as used herein, refers to aging the coverin a fixed environment for a fixed length of time.

This cover layer is set to a surface hardness, expressed as the Shore Dhardness, of preferably from 58 to 65, and more preferably from 59 to62. If the surface hardness of the cover layer is too low, the spin rateon shots with a driver may increase, resulting in a shorter distance. Onthe other hand, if the surface hardness of the cover layer is too high,the ball may have a poor feel and the resilience and durabilityattributes of the urethane material may diminish.

The hardness of this cover is preferably set so as to be equal to orgreater than the hardness of the intermediate layer; i.e., coverhardness z intermediate layer hardness. If the cover hardness is lowerthan the intermediate layer hardness, the ball may have a hard and poorfeel on impact, which may make it impossible to achieve the objects ofthe invention.

The cover layer has a rebound resilience of generally at least 35%,preferably at least 40%, more preferably at least 45%, and even morepreferably at least 47%. Because thermoplastic polyurethanes basicallydo not have such an outstanding resilience, strict selection of theabove rebound resilience is preferred. If the rebound resilience of thecover layer is too low, the golf ball may undergo a large decline indistance. On the other hand, if the cover layer has an excessively highrebound resilience, the initial velocity on puts and on shots of lessthan 100 yards requiring control may be too high, and may not result ina good feel on impact for the golfer. In the present invention, “reboundresilience” refers to the rebound resilience obtained in accordance withJIS K7311.

The thickness of this cover, although not subject to any particularlimitation, is set to preferably at least 0.4 mm, and more preferably atleast 0.7 mm. The upper limit, although not subject to any particularlimitation, is set to preferably not more than 1.5 mm, and morepreferably not more than 1.3 mm. If the cover thickness is too large,the rebound may decrease. On the other hand, if the cover thickness istoo small, the durability may decrease.

The structure of the cover is not limited to one layer; if necessary, acover of two or more layers may be formed with materials havingdifferent properties. In this case, it is recommended that the coverhave at least one layer which is formed of the above resin blendcomposed primarily of components (f) and (g), and that the hardness andthickness be adjusted so that these values for the overall cover fallwithin the above-indicated ranges.

In the golf ball of the present invention, to further enhance theaerodynamic properties and improve the distance, as in ordinary golfballs, it is preferable for numerous dimples to be formed on the surfaceof the cover. By optimizing such parameters as the number of dimpletypes and the total number of dimples, through synergistic effects withthe above-described ball construction, there can be obtained a golf ballhaving a more stable trajectory and an improved distance performance.Moreover, to improve the design and durability of the golf ball, varioustreatments such as surface treatment, stamping and painting may becarried on the cover.

Here, it is recommended that the number of dimple types, which refers tothe number of dimple types of mutually differing diameter and/or depth,be preferably at least two types, and more preferably at least threetypes. It is recommended that the upper limit be not more than eighttypes, and in particular not more than six types.

Because the golf ball of the present invention, owing to theabove-described ball construction, tends to have a decreased spin rateat the time of impact, and thus a lower trajectory, it is preferable tocarry out dimple design in such a way as to enable a large lift to beobtained.

First, the total number of dimples is set to preferably at least 250,and more preferably at least 270. The upper limit is preferably set tonot more than 392, and more preferably not more than 360. If the totalnumber of dimples is too low or too high, an optimal lift may not beachieved and the ball may travel a less than desirable distance.

Nor is any particular limitation imposed on the geometrical arrangementof the dimples; use may be made of a known arrangement, such as anoctahedral or an icosahedral arrangement. At this time, from thestandpoint of reducing variability in the flight of the ball, preferreduse may be made of a dimple arrangement such that the surface of theball has thereon not even a single great circle which intersects nodimples. The dimple shapes are not limited to circular shapes, and mayalso be suitably selected from among polygonal, teardrop, oval and othershapes. The dimple diameter (in polygonal shapes, the diagonal length)be set to preferably at least 1 mm, and more preferably at least 2 mm.The upper limit is set to preferably not more than 8 mm, and morepreferably not more than 7 mm.

It is recommended that the dimple surface coverage, from the standpointof reducing air resistance, be at least 75%, and especially at least79%. This surface coverage can be increased by raising the number ofdimples formed, interspersing a plurality of dimples types of differingdiameter, and using dimple shapes in which the distance betweenneighboring dimples (land width) becomes substantially 0.

The total volume of the dimples refers to the sum of the volumes ofthose portions circumscribed by dimple walls and the curved surfaces ofland areas on the ball surface. This total volume is preferably set tofrom 400 to 750 mm³, and especially from 450 to 700 mm³.

The golf ball of the invention may be made to conform with the Rules ofGolf for competitive play, and may be formed to a diameter of not lessthan 42.67 mm. It is generally suitable to set the weight to not lessthan 45.0 g, and preferably not less than 45.2 g, but not more than45.93 g.

Although not subject to any particular limitation, the golf ball of thepresent invention has an overall ball deflection, when compressed undera final load of 1,275 N (130 kgf) from an initial load state of 98 N (10kgf), of preferably at least 2.5 mm, and more preferably at least 2.7mm. The upper limit is preferably not more than 4.0 mm, and morepreferably not more than 3.7 mm. If the deflection is too small, thefeel on impact may worsen and, on long shots such as with a driver inwhich the ball incurs a large deformation, may subject the ball to anexcessive rise in the spin rate, shortening the distance traveled by theball. On the other hand, if the deflection is too large, the ball mayhave a dead feel and a less than adequate rebound, shortening thedistance traveled, in addition to which the ball may have a poordurability to cracking on repeated impact.

Although not subject to any particular limitation, it is desirable forthe golf ball of the invention to exhibit a decline in initial velocityone year after manufacture relative to the initial velocity one weekafter manufacture (after molding) of preferably not more than 0.5 m/s,and more preferably not more than 0.4 m/s. Such an initial velocity maybe achieved by adjusting the formulation of the intermediatelayer-forming material in accordance with the core and cover within therange set forth in the present invention. As used herein, “initialvelocity” refers to the value measured using an initial velocitymeasuring apparatus of the same type as the USGA drum rotation-typeinitial velocity instrument approved by the R&A. The specificmeasurement conditions are given in the examples described below.

EXAMPLES

The following Examples and Comparative Examples are provided by way ofillustration and not by way of limitation.

Examples 1 to 3, Comparative Examples 1 to 4 Formation of Core

Solid cores were fabricated by preparing the rubber compositions shownin Table 1 below, then molding and vulcanizing at 155° C. for 15minutes.

TABLE 1 Formulation No. 1 No. 2 Formulation Polybutadiene 100 100 (pbw)Dicumyl peroxide 1.2 1.2 Zinc oxide 18.02 19.142,2′-Methylenebis(4-methyl-6-t- 0.1 0.1 butylphenol) Zinc diacrylate32.71 29.99 Zinc salt of pentachlorothiophenol 0.10 0.10

Details on the materials in Table 1 are given below.

-   Polybutadiene: Available under the trade name “BR 730” from JSR    Corporation.-   Dicumyl peroxide: Available under the trade name “Percumyl D” from    NOF Corporation.-   Zinc oxide: Available from Sakai Chemical Industry Co., Ltd.-   2,2′-Methylenebis(4-methyl-6-t-butylphenol): Available under the    trade name “Nocrac NS-6” from Ouchi Shinko Chemical Industry Co.,    Ltd.-   Zinc diacrylate: Available from Nihon Jyoryu Kogyo Co., Ltd.-   Zinc salt of pentachlorothiophenol:    -   Available from Tokyo Kasei Kogyo Co., Ltd.

Formation of Intermediate Layer and Cover

Next, an intermediate layer and a cover of the formulations shown belowwere successively injection-molded around the core obtained as describedabove, thereby producing three-piece solid golf balls (of three types inthe examples according to the invention and of four types in thecomparative examples) having the core, intermediate layer and covercombinations shown in Table 3. At this time, the dimples shown in FIG. 1were formed on the cover surface. Details of these dimples are shown inTable 2.

Formation of the covers in Working Examples 1 to 4 and ComparativeExamples 1 to 4 was carried out as follows.

First, each of the following cover materials was mixed in a nitrogenenvironment with a twin-screw extruder to give a cover resin blend inpellet form (length, 3 mm; diameter, 1 to 2 mm). The cover material wasthen injection-molded around a core to form a cover.

Intermediate Layer Formulation A

Nucrel AN4319 (acid content, 8.0 wt %; 100 parts by weight estercontent, 17.0 wt %) Magnesium stearate 100 parts by weight Magnesiumoxide 2.8 parts by weight Polytail 4.0 parts by weight Degree ofneutralization: 110.4 mol % Shore D hardness: 50

Intermediate Layer Formulation B

Nucrel AN4319 (acid content, 8.0 wt %; 30 parts by weight ester content,17.0 wt %) Nucrel AN4221C (ester content, 0.9 wt %) 60 parts by weightDynaron 6100P 10 parts by weight Magnesium stearate 60 parts by weightMagnesium oxide 1.3 parts by weight Degree of neutralization: 80.4 mol %Shore D hardness: 56

Intermediate Layer Formulation C

Himilan H1605 68.8 parts by weight Himilan AM7331 31.3 parts by weightBehenic acid 18 parts by weight Calcium hydroxide 2.3 parts by weightPolytail 2.0 parts by weight Degree of neutralization: 56.0 mol % ShoreD hardness: 56

Cover Layer Formulation A

Pandex T8260 50 parts by weight Pandex T8295 50 parts by weightPolyisocyanate compound 7.5 parts by weight Elastomer 11 parts by weightPolyethylene wax 1 part by weight Titanium oxide 3 parts by weight ShoreD hardness: 59

Cover Layer Formulation B

Pandex T8260 100 parts by weight Polyisocyanate compound 7.5 parts byweight Elastomer 11 parts by weight Polyethylene wax 1 part by weightTitanium oxide 3 parts by weight Shore D hardness: 61

Cover Layer Formulation C

Himilan H1557 75 parts by weight Himilan H1855 25 parts by weightPolyethylene wax 1 parts by weight Magnesium stearate 1.8 parts byweight Titanium oxide 3.8 parts by weight Shore D hardness: 58

Cover Layer Formulation D

Pandex T8295 100 parts by weight Polyisocyanate compound 7.5 parts byweight Elastomer 11 parts by weight Polyethylene wax 1 part by weightTitanium oxide 3 parts by weight Shore D hardness: 57

Cover Layer Formulation E

Pandex T8295 75 parts by weight Pandex T8290 25 parts by weightPolyisocyanate compound 7.5 parts by weight Elastomer 11 parts by weightPolyethylene wax 1 part by weight Titanium oxide 3 parts by weight ShoreD hardness: 54

Details on the materials used in above Intermediate Layer Formulations Ato C and Cover Layer Formulations A to E are given below.

-   Nucrel AN4319: An olefin-unsaturated carboxylic acid-carboxylic acid    ester terpolymer available from DuPont-Mitsui Polychemicals Co.,    Ltd.-   Nucrel AN4221C: An olefin-unsaturated carboxylic acid copolymer    available from DuPont-Mitsui Polychemicals Co., Ltd.-   Himilan AM7331: An ionomer resin in the form of a sodium    ion-neutralized ethylene-methacrylic acid-acrylic acid ester    copolymer available from DuPont-Mitsui Polychemicals Co., Ltd.-   Himilan 1605: An ionomer resin in the form of a sodium    ion-neutralized ethylene-methacrylic acid copolymer available from    DuPont-Mitsui Polychemicals Co., Ltd.-   Himilan 1557: An ionomer resin in the form of a zinc ion-neutralized    ethylene-methacrylic acid copolymer available from DuPont-Mitsui    Polychemicals Co., Ltd.-   Himilan 1855: An ionomer resin in the form of a zinc ion-neutralized    ethylene-methacrylic acid copolymer available from DuPont-Mitsui    Polychemicals Co., Ltd.-   Dynaron 6100P: A CEBC-type olefinic thermoplastic elastomer    available from JSR Corporation.-   Pandex T8260: A MDI-PTMG type thermoplastic polyurethane material    available from DIC Bayer Polymer. Durometer D resin hardness, 56.    Rebound resilience, 45%.-   Pandex T8295: A MDI-PTMG type thermoplastic polyurethane material    available from DIC Bayer Polymer. JIS-A resin hardness, 97. Rebound    resilience, 44%.-   Pandex T8260: A MDI-PTMG type thermoplastic polyurethane material    available from DIC Bayer Polymer. JIS-A resin hardness, 93. Rebound    resilience, 52%.-   Elastomer: Hytrel 4001, available from DuPont Toray Co., Ltd.-   Behenic acid: Available as “NAA-222S (powder)” from NOF Corporation.-   Magnesium stearate: Available as “Nissan Magnesium Stearate” from    NOF Corporation.-   Polyisocyanate compound: 4,4′-Diphenylmethane diisocyanate.-   Polyethylene wax: Available as “Sanwax 161P” from Sanyo Chemical    Industries, Ltd.-   Polytail: A low-molecular-weight polyolefin polyol available from    Mitsubishi Chemical Corporation.-   Magnesium oxide: A high-activity type magnesium oxide available as    “Micromag 3-150” from Kyowa 1.0 Chemical Industry.-   Calcium hydroxide: Available as “CLS-B” from Shiraishi Calcium    Kaisha, Ltd.-   Titanium oxide: Available under the trade name “Tipaque R550” from    Ishihara Sangyo Kaisha, Ltd.

TABLE 2 Total Diameter Depth volume No. Number (mm) (mm) V₀ (mm³) SR VR1 12 4.60 0.15 0.47 568 0.81 0.784 2 234 4.40 0.15 0.47 3 60 3.80 0.140.47 4 12 3.50 0.13 0.47 5 12 2.50 0.10 0.47 Total 330

Dimple Definitions

-   Diameter: Diameter of flat plane circumscribed by edge of dimple.-   Depth: Maximum depth of dimple from flat plane circumscribed by edge    of dimple.-   V₀: Spatial volume of dimple below flat plane circumscribed by    dimple edge, divided by volume of cylinder whose base is the flat    plane and whose height is the maximum depth of dimple from the base.-   Total volume: Sum of volume of portions circumscribed by dimple    walls and curved surfaces of land areas on ball surface.-   SR: Sum of individual dimple surface areas, each defined by the    surface area of the flat plane circumscribed by the edge of a    dimple, as a percentage of surface area of ball sphere were it to    have no dimples thereon.-   VR: Sum of volumes of individual dimples formed below flat plane    circumscribed by the edge of the dimple, as a percentage of volume    of ball sphere were it to have no dimples thereon.

For each of the golf balls obtained, various properties, including thethickness, hardness and deflection of the respective layers, and theflight performance and scuff resistance were measured by the followingmethods. The results are shown in Table 3.

Measuring the Ball Properties Deflection (mm) of Core and Finished Ball

The core and the finished ball were placed on a hard plate, and thedeflection when compressed under a final load of 1,275 N (130 kgf) froman initial load state of 98 N (10 kgf) was measured.

Deflection (mm) of Intermediate Layer

A sphere composed of the core encased by the intermediate layer wasplaced on a hard plate, and the deflection when compressed under a finalload of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf)was measured.

Cover Hardness and Intermediate Layer Hardness

The Shore D hardness of the cover layer alone and the intermediate layeralone, as measured in accordance with ASTM D-2240.

Flight Performance

-   Distance and Spin Rate on Shots with a W#1: The distance traveled by    the ball when hit at a head speed of 50 m/s with a W#1 mounted on a    golf swing robot was measured. A Tour Stage X-Drive 701 driver (2009    model; loft, 8.5°) manufactured by Bridgestone Sports Co., Ltd. was    used as the club. The spin rate was obtained by using an apparatus    for measuring initial conditions to measure the ball immediately    after being hit in the same way.-   Spin Rate on Shots with a Wedge: The spin rate was obtained by using    an apparatus for measuring initial conditions to measure the ball    immediately after being hit at a head speed of 24 m/s with a    pitching wedge mounted on a golf swing robot. A J's Classical    Edition pitching wedge manufactured by Bridgestone Sports Co., Ltd.    was used as the club.

Scuff Resistance

Golf balls were held at a temperature of 23° C., 13° C. or 0° C. and therespective balls were hit at a head speed of 33 m/s using a non-platedpitching wedge mounted on a swing robot machine, following which damagefrom the impact was visually rated. The ball was assigned a scuffresistance rating of “Good” when six or more out of ten judges thoughtthe ball could be used again, and was assigned a scuff resistance ratingof “NG” when five or fewer judges thought the ball was no longer fit foruse.

Initial Velocity

The initial velocity one week after production (molding) of theresulting ball (Initial Velocity A), and the initial velocity one yearafter production (Initial Velocity B) were measured by the followingmethod, and the decrease in initial velocity when one year had elapsedfollowing production was determined.

Method of Measuring Initial Velocity:

The initial velocity was measured under the following conditions usingan initial velocity measuring apparatus of the same type as the USGAdrum rotation-type initial velocity instrument approved by the R&A. Theball was hit using a 250-pound (113.4 kg) head (striking mass) at animpact velocity of 143.8 ft/s (43.83 m/s). Ten balls were each hit fourtimes. The time taken for the balls to traverse a distance of 6.28 ft(1.91 m) was measured and used to compute the initial velocity. Inconducting this test, the balls were held isothermally at a temperatureof 23±1° C. for at least 3 hours, then tested in a room temperature(23±2° C.) chamber.

TABLE 3 Example Comparative Example 1 2 3 4 1 2 3 4 Core Formulation No.1 No. 2 No. 1 No. 2 No. 1 No. 2 No. 1 No. 1 Diameter (mm) 38.1 38.1 38.138.1 38.1 38.1 38.1 38.1 Deflection (mm) 3.4 3.7 3.4 3.7 3.4 3.7 3.4 3.4Intermediate Formulation A B A B A C A B layer Thickness (mm) 1.31 1.311.31 1.31 1.31 1.31 1.31 1.31 Shore D hardness 50 56 50 56 50 56 50 56Deflection (mm) 3.2 3.2 3.2 3.2 3.2 3.1 3.1 3.2 Cover Formulation A A BB C A D E Thickness (mm) 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 Shore Dhardness 59 59 61 61 58 59 57 54 Ball Diameter 42.70 42.70 42.70 42.7042.70 42.70 42.70 42.70 Deflection (mm) 2.9 2.9 2.9 2.9 2.9 2.9 2.9 3Dimples FIG. 1, FIG. 1, FIG. 1, FIG. 1, FIG. 1, FIG. 1, FIG. 1, FIG. 1,Table 2 Table 2 Table 2 Table 2 Table 2 Table 2 Table 2 Table 2Performance Spin rate with 2550 2530 2520 2500 2650 2680 2700 2900 W#1(rpm) Spin rate with 5700 5700 5500 5500 5700 5700 5900 6100 wedge (rpm)Distance with 235 234 240 241 230 230 230 226 W#1 (m) Scuff resistanceGood Good Good Good NG Good Good Good Initial velocity A 77.30 77.3077.30 77.30 77.30 77.20 77.30 77.30 Initial velocity B 76.50 77.00 76.5077.00 76.50 46.90 76.50 77.00 Initial velocity −0.80 −0.30 −0.80 −0.30−0.80 −0.30 −0.80 −0.30 difference (A − B)

As shown in Table 3, the golf balls of the present invention hadrelatively low spin rates on shots with a driver, enabling the distancetraveled by the ball to be increased. The same balls also had good spinrates on shots with a wedge and thus an excellent controllability.Moreover, the inventive golf balls had an excellent scuff resistance anda good durability.

1. A golf ball comprising a core, at least one intermediate layer and acover, wherein the intermediate layer has a Shore D hardness of from 40to 60 and is formed primarily of a resin mixture having a degree ofneutralization of at least 70% and including: 100 parts by weight of aresin component composed of, in admixture, a base resin of (a) anolefin-unsaturated carboxylic acid random copolymer and/or a metal ionneutralization product of an olefin-unsaturated carboxylic acid randomcopolymer blended with (b) an olefin-unsaturated carboxylicacid-unsaturated carboxylic acid ester random terpolymer and/or a metalion neutralization product of an olefin-unsaturated carboxylicacid-unsaturated carboxylic acid ester random terpolymer in a weightratio of from 100:0 to 0:100, and (e) a non-ionomeric thermoplasticelastomer in a weight ratio of from 100:0 to 50:50; (c) about 50 toabout 150 parts by weight of a fatty acid and/or fatty acid derivativehaving a molecular weight of from 228 to 1500; and (d) about 0.1 toabout 17 parts by weight of a basic inorganic metal compound capable ofneutralizing un-neutralized acid groups in the base resin and component(c), and the cover has a Shore D hardness of from 58 to 65 and is formedby injection molding a single resin blend composed primarily of (f) athermoplastic polyurethane and (g) a polyisocyanate compound in at leastsome portion of which all the isocyanate groups on the molecule arepresent in an unreacted state.
 2. The golf ball of claim 1, wherein thehardness of the cover is equal to or greater than the hardness of theintermediate layer.
 3. The golf ball of claim 1, wherein the resin blendwhich forms the cover includes (h) a thermoplastic elastomer other thana thermoplastic polyurethane.
 4. The golf ball of claim 3, wherein someportion of the isocyanate groups in the polyisocyanate compound (g)included in the resin blend prior to injection molding form bonds withactive hydrogens in component (f) and/or component (h), and theremaining isocyanate groups are present within the resin blend in anunreacted state.
 5. The golf ball of claim 3, wherein the components inthe resin blend which forms the cover have a compositional ratio,expressed as a weight ratio, of (f):(g):(h)=100:2 to 50:0 to
 50. 6. Thegolf ball of claim 3, wherein the components in the resin blend whichforms the cover have a compositional ratio, expressed as a weight ratio,of (f):(g):(h)=100:2 to 30:8 to
 50. 7. The golf ball of claim 1, whereinthe resin blend which forms the cover has a melt mass flow rate (MFR)value at 210° C. of at least 5 g/10 min.
 8. The golf ball of claim 1,wherein the polyisocyanate compound of component (g) is one or morepolyisocyanate compound selected from the group consisting of4,4′-diphenylmethane diisocyanate, 2,4- (or) 2,6-toluene diisocyanate,p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylenediisocyanate, tetramethylxylene diisocyanate, hydrogenated xylylenediisocyanate, dicyclohexylmethane diisocyanate, tetramethylenediisocyanate, hexamethylene diisocyanate, isophorone diisocyanate,norbornene diisocyanate, trimethylhexamethylene diisocyanate and dimeracid diisocyanate.
 9. The golf ball of claim 1, wherein thepolyisocyanate compound of component (g) is one or more polyisocyanatecompound selected from the group consisting of 4,4′-diphenylmethanediisocyanate, dicyclohexylmethane diisocyanate and isophoronediisocyanate.
 10. The golf ball of claim 3, wherein the thermoplasticelastomer of component (h) is one or more thermoplastic elastomerselected from the group consisting of polyester elastomers, polyamideelastomers, ionomer resins, styrene block elastomers, hydrogenatedstyrene-butadiene rubbers, styrene-ethylene/butylene-ethylene blockcopolymers and modified forms thereof,ethylene-ethylene/butylene-ethylene block copolymers and modified formsthereof, styrene-ethylene/butylene-styrene block copolymers and modifiedforms thereof, ABS resins, polyacetals, polyethylenes and nylon resins.11. The golf ball of claim 3, wherein the thermoplastic elastomer ofcomponent (h) is one or more selected from the group consisting ofpolyester elastomers, polyamide elastomers and polyacetals.
 12. The golfball of claim 1, wherein the ball has a plurality of dimples formed on asurface thereof, which dimples number in all from 250 to 392 and have atotal volume of from 400 to 750 mm³.